Conduit



June 5, 1934. w. A. KRANER 1,961,974

CONDUIT Filed May 2, 1932 /Z' 5 FIE IE A TTORNEYS.

Patented June 5, I934 CONDUIT Warren A. Kraner, San Francisco, Calif.,assignor to Cement Wrapped Pipe Company, Ltd San Francisco, Calif., acorporation of Arizona Application May 2, 1932, Serial No. 608,728

5 Claims.

This invention relates generally to conduits or piping, such as areemployed in conjunction with water and gas distribution systems or oillines.

In the past it has been noted that subterranean metallic conduits orpiping employed in conjunction with fluid distribution systems, havefrequently been subject to rapid deterioration. This deterioration ispartly due to common rusting of the steel pipe, and also to corrosivechemicals which may be in the fiuid conveyed or in the water with whichthe outer surface of the pipe comes into contact. However the more rapiddeterioration often experienced has been found due largely toelectrolysis. Electrolysis results from electrical current flow betweenthe metal conduit and the surrounding moist ground, and such current maybe induced artificially in certain installations, or may occur fromnatural causes.

As faras I am aware there is no commercially practical metal conduit nowin the market, capable of withstanding the deleterious effects ofelectrolysis. A coating of asphaltic material upon the outer surface ofthe pipe has been found to have very little beneficial effect, eventhough a sheathing of tar paper is employed. Likewise steel conduitjacketed with reinforced concrete has been found subject toelectrolysis.

It is an object of the present invention to provide a protective jacketfor metal conduit or piping which will afford an effective protectionagainst deterioration by electrolysis.

It is a further object of the invention to provide a protective jacketof the above character which will not be prohibitive in cost, and whichwill therefore have general commercial application.

Further objects of the invention will appear from the followingdescription in which the preferred embodiment of the invention has beenset forth in detail in conjunction with the accompanying drawing.

Referring to the drawing:

Figure l is a plan view, illustrating certain steps in the method ofapplying a protective jacket in accordance with the present invention.

Fig. 2 is a view similar to Fig. 1, but illustrating further steps inthe method.

Fig. 3 is an enlarged cross sectional detail, illustrating my protectivecoating in its preferred form.

Referring first to Figure 3, the protective jacket shown therein hasbeen applied to the steel wall 10 of an ordinary fluid conduit. Thisprotective jacket consists of an outer layer 11 of concrete, withinwhich a metal reinforcement 12 is embedded. The concrete layer is shownapplied to the outer surface of a sheathing 13 of fibrous material, andinterposed between sheathing 13 and the outer surface of the metal wall10, there is a coating 14 of material having relatively high dielectricstrength.

Coating 14.- is preferably of such material that it will form acontinuous unbroken water-tight membrane, and one which has sufficientresili- 5 ence to stretch and flex a certain amount without cracking.Certain coating materials of this character are now available on themarket, which are formed of an asphaltic base. The sheathing 13 ispreferably of such material that it will not deteriorate when subjectedto moisture, as for example a paper made largely of asbestos fibreimpregnated with asphaltic material. Coating 14 is adhered to the outersurface of the metal walls 10, while sheathing 13 is in turn bonded tothe coating 14. The concrete layer 11 is in in tjmate or close contactwith the outer surface of sheathing 13.

A jacket such as has been described with reference to Fig. 3 can beformed as follows:-The coating 14 is first applied to the outer metalsurface of the pipe, as by dipping the pipe into the coating material,while the material is in liquid condition. After this coating hassolidified, the coated pipe, indficated generally at 16 in Fig. 1, isrotated between suitable centers, and the sheathing 13 is then appliedin the form of a strip 1'7 wrapped spiraHy about the pipe. As the stripis being wrapped upon the pipe, its inner surface is covered w thadditional coating material, as by way of thenozzle 18. The edges ofadjacent convolutions of strip 17 are preferably overlapped as shown inFig. 1.

After the pipe has been completely wrapped with strip 17 to form thesheathing 13, the next step is to apply the concrete jacket 11. Inapplying such a layer of concrete, I preferably utilize the apparatusand method disclosed in my co-pending application, Ser. No. 537,009filed May 13, 1931. Thus as indicated in Fig. 2, while the pipe is beingrotated between suitable centers,

a strip 19 of plastic concrete is wrapped spirally upon the pipe, andembedded in this strip of concrete there is a suitable metallicreinforcement 21, as for example a strip of metallic screening.Screening 21 is maintained under tension while the concrete strip 19 isapplied, so that after application the concrete layer 11 is held intight engagement with the outer surface of the sheathing 13.

A protective jacket such as described above forms an effectiveelectrical insulator for the exterior of the metal conduit. This hasbeen demonstrated by tests in which the exterior of the pipe wasentirely immersed in brine solution. The concrete layer 11 affordsmechanical protection, and at the same time prevents free flow ofchemical containing liquid into contact with the sheathing 13. Sheathing13, while it affords some dielectric strength of itself, affords aprotection for the inner coating 14. If the concrete layer were applieddirectly to coating 14 without the intervening sheathing 13, themembrane afforded by coating 14 might be disrupted by particles of theconcrete, and might be disrupted to form fine cracks upon deflecting themetal wall of the pipe. When sheathing 13 is employed,coating 14 remainsintact as a continuous membrane, even though the pipe may be bentslightly in a direction lateral of its axis, or even though the walls ofthe pipe may be slightly deflected. Likewise the presence of sheathing13 largely prevents penetration of liquids into contact with coating 14.

I claim:

1. In conjunction With a metall c conduit, a protective jacketconsisting of a coating of dielectric material applied upon the outersurface of the conduit, a sheathing of fibrous material applied andbonded to said coating, and a layer of concrete covering sa'd sheathing.

2. In conjunction with a metallic conduit, a

protective jacket consisting of a coating of asphaltic material appliedupon the outer surface of the conduit to form a moisture proofdielectric medium, a sheathing of fibrous material applied and bonded.tosaid coating, and a layer of concrete applied upon said fibrousmaterial.

3. In conjunction with a metallic conduit, a protective jacketconsisting of a coating of asphaltic maten'al applied upon the outersurface of the conduit to form a moisture proof electrical insulatingmedium, a sheathing consisting of asbestos fibre impregnated withasphaltic material, applied and bonded to said coating, and a layer ofconcrete applied upon said sheathing.

4. In conjunction with a metallic conduit, a protective jacketconsisting of a water impermeable and elastic coating of dielectricmaterial applied upon the outer surface of the conduit, a sheathingconsisting of asbestos fibre impregnated with asphaltic material,applied and bonded to said coating, and a layer of concrete applied uponsaid fibrous material.

5. In conjunction with a metallic conduit, a protective jacket consistngof a coating of dielectric material applied upon the outer surface ofthe conduit, said coating being impermeable to water and relativelyflexible, a sheathing of fibrous material applied and bonded to saidcoating, and a relatively r.'gid layer of reinforced concrete appliedupon said sheathing.

WARREN A. KRANER.

